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Research On Vibration Coupling Characteristics Of Ship Damping Composite Bulkhead Structure

Posted on:2024-12-08Degree:DoctorType:Dissertation
Country:ChinaCandidate:F WangFull Text:PDF
GTID:1522307325964369Subject:Naval Architecture and Marine Engineering
Abstract/Summary:PDF Full Text Request
Under the background of the rapid development of globalization,IMO and the related organizations have the strict standards for the design and manufacture of marine equipment,which in turn puts forward higher requirements for ship vibration and noise control.Ships may produce different strengths of vibration under the effect of power system,wind and waves during the sailing,which not only reduces the comfort of travelling,but also affects the stable operation of precision equipment on board.Besides,the noise caused by vibration is easy to leak the location of the ship,which seriously affects its concealment and safety.Therefore,the effective technologies to suppress the ship vibration and noise and then optimize the mechanical environment of ship structures has become the key to enhance ship performance.Considering the diversity of ship excitation forces and the complexity of the structure,it is an effective strategy to solve the vibration problems of the ship structures through damping materials.In this thesis,the vibration coupling characteristics of a ship bulkhead structure coated with a viscoelastic damping material are investigated,and the research content is described as follows:(1)The damping characteristics and mechanism viscoelastic damping materials is carried out from the macro and microscopic perspectives analytically.A novel viscoelastic damping material with wide temperature domain is prepared.Through the dynamic performance test,the variation of its damping parameters with temperature and frequency is analyzed.The results show that the loss factor of the material is above 0.25 in the temperature range from 0 °C to120 °C,and reaches a maximum value of 0.53 at 52.92 °C.When the material enters the glass transition region,its energy storage modulus decreases the most;the loss factor exhibits a tendency of increasing and then decreasing,and reaches a maximum at Tg.At a constant temperature,the energy storage modulus and Tg gradually increase with increasing frequency,and the loss factor first increases and then decreases with increasing frequency.A model of damped composite beam structure based on the prepared viscoelastic damping material is established to investigate the effect of the damping layer thickness on the vibration characteristics of the composite beam structure.The intrinsic frequency of the composite beam structure and the thickness of the damping layer are nonlinearly and negatively correlated.When the thickness of the damping layer is equal to the thickness of the substrate,the change of the intrinsic frequency of the first order is the most significant,and its change rate reaches 4.54%,which shows that the damping layer has a significant effect on the vibration characteristics of the structure.(2)Based on the theoretical method of vibration calculation of elastic beam structure,the intrinsic frequency and modal equations of elastic beam structure are derived and the first10th-order intrinsic frequency of cantilever beam are utilized to evaluated the model validity.The comparison of the simulation results with the finite element software and the experimental results shows that the calculation results based on the proposed model are in good agreement with the simulation and the experimental results,in which the maximum deviation rate with the simulation results of the finite element software is only 1.44%.Based on the above results,the dynamic model of viscoelastic damped composite beam structure is established.Through introducing the auxiliary variables,the dynamic equations of viscoelastic damped composite structure are converted from differential-integral type to differential type,which can be solved through the state-space method.The effectiveness of the method is verified through the comparison of the calculation examples and experiments.The results also suggest that assembling the total mass matrix and total stiffness matrix of the viscoelastic damped composite beam model,the dynamics model of the beam can be extended to the viscoelastic damped composite structures of arbitrary shapes,such as plates and shells,which effectively reduces the complexity of the numerical simulation of damped composite structures.(3)Based on the actual dimensions of “Yinshun” ship,a bulkhead structure model is constructed and based on the finite element method to study the vibration modal characteristics.The dynamic performance and the modal characteristics of the bulkhead structure under different working conditions are investigated.It can be found that when the ballast water is considered,the presence of ballast water has a significant effect on the vibration characteristics of the bulkhead structure,which can be observed that the change rate of the wet mode intrinsic frequency decreases with the increase of the modal order.Considering the frequency dependence of the damping characteristics of the viscoelastic damping material,the harmonic response analyses of the bulkhead structures with uncoated and coated viscoelastic damping materials are carried out to investigate the vibration coupling characteristics of the ship’s damped composite bulkhead structure,and then the information interaction relationship between the forces and displacements of different materials in the coupled vibration of the composite bulkhead is revealed.The results show that there is a phase difference between the stresses and strains of different materials in the damped composite bulkhead structure.In particular,the phase difference between the stresses and strains can be as high as 53.118° in the interior of the damping layer.Conversely,the phase difference in the interior of the steel plate in the bulkhead structure is extremely small.The results reveal the differences in the vibrational coupling between different materials in the composite bulkhead structure.(4)Based on the model similarity theory,the modal parameter similarity relationship and its expression is conducted.According to the ratio between the size of the real ship and the size of the experimental model,the modal parameter similarity coefficient K=320 is obtained.Based on it,the ship bulkhead structure vibration test platform is designed and constructed.The experimental results show that:(a)the measured experimental model intrinsic frequency and the theoretically calculated intrinsic frequency have a good agreement,with a maximum deviation of6.4%,which verifies the correctness of the numerical calculation results;(b)the viscoelastic damping composite bulkhead has a remarkable effect on vibration suppression.The frequency response amplitude significantly lower than that of the bulkhead structural model uncoated with viscoelastic damping material,and the frequency response curve is smoother,with a more rounded peak,which fully proves the effectiveness of viscoelastic damping material in vibration control.This thesis carries out the study of damping characteristics,composite structure theoretical calculation method,numerical simulation and experimental comparative verification analysis,and then analyzes the vibration coupling characteristics of the ship damped composite bulkhead structure through the combination of theoretical analysis and experimental verification.These research work elucidates the validity of the viscoelastic damping material in vibration reduction,and reveals the vibration coupling characteristics of the ship damped composite bulkhead structure.
Keywords/Search Tags:Ship composite bulkheads, Vibration control, Finite element method, Modal analysis, Viscoelastic damping materials
PDF Full Text Request
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